Poor medication adherence is a serious public health problem in diabetes and may play a role in perpetuating inadequate risk factor control, particularly among minority and socioeconomically- disadvantaged patients. Extant medical literature has underestimated rates of nonadherence because it relies almost exclusively on adherence estimates derived from refill history among ongoing users, and thus fails to account for the large number of patients who are prescribed new therapies but never become ongoing users. We show preliminary evidence that one quarter of treatment-naove patients prescribed a new cardiometabolic medication (antihypertensive, antilipemic or antihyperglycemic) never fill (primary non-adherence) or never refill (early non-persistence) the new prescription and thus fail to become ongoing users. A more comprehensive understanding of adherence is needed; one that includes, first, all stages of medication adherence, from new prescription to therapy discontinuation and, second, how the stages of adherence shape social disparities in clinical outcomes. We propose a longitudinal study of diabetic patients prescribed a new cardiometabolic medication to assess social disparities in medication adherence, explanatory factors and clinical consequences. This new prescription design will take advantage of a pharmacy management system that electronically records physicians' prescription orders, dose changes, discontinuation orders and incident side effects. Study subjects will include members of the Kaiser Permanente Northern California Diabetes Registry, a large, well-characterized, ethnically-diverse, insured population of managed care patients with diabetes mellitus. Socially-disadvantaged patients are well represented in this study population, which has uniform access to and quality of care, unlike most population-based samples. Given that 92% of Americans with diabetes have health insurance, findings from this insured population should have broad public health relevance. Given this will be the first, large epidemiological study to assess primary medication adherence, it will provide a more comprehensive understanding of how social disparities in medication adherence shape disparities in diabetes-related risk factor control and inform the design of future interventions aimed at reducing health disparities. PUBLIC HEALTH RELEVANCE: Project Narrative This study will evaluate whether diabetes, blood pressure and cholesterol medications, are taken by patients with diabetes as prescribed (adherence), emphasizing social patterns in adherence, clinical consequences and reasons for differences in therapy initiation, maintenance and discontinuation. We will take advantage of new electronic prescribing data to evaluate medication adherence starting from the point the doctor writes the new prescription. Study findings should be generalizable to the 92% of Americans with diabetes who have health insurance, and provide a more comprehensive understanding of medication adherence in diabetes.